Apoptosis in the basal ganglia of the developing human nervous system

Programmed cell death (PCD) plays a crucial role in the development of the central nervous system through controlling neuronal numbers and adequate synaptic connections. PCD has been considered to occur in the form of apoptosis. To examine how apoptosis occurs in the developing human brain, we performed a morphometric TUNEL study, using a commercially available kit (ApopTag Kit, Oncor Inc.). We examined apoptotic cells in the basal ganglia of 47 fetuses and newborns without macroscopical and microscopical evident congenital anomalies. Gestational age ranged from 12 to 40 weeks. The numerical density as well as the labeling index of TUNEL-positively labeled nuclei were evaluated. In the caudate nucleus and putamen, TUNEL-labeled cells were observed around the 12th week of gestation. The numerical density of total cells was significantly decreased, whereas the labeling index of apoptotic cells was significantly increased with advanced gestational age. In the globus pallidus, the numerical density of total cells decreased with advancing gestational age, while the labeling index of apoptotic cells increased between the 20th and 28th week, followed by a decrease until the 40th week. The analysis of TUNEL-positive cells revealed a different reaction pattern for the various basal ganglia with regard to the timing and degree of the apoptotic process in regulating cell numbers.